Heat transfer between a body and its surrounding environment is an inherent response to a non-uniform temperature distribution between the body and the environment. Limiting heat transfer between a body and its environment is highly desirable in many situations. Such heat transfer is the result of conduction, convection, and radiation. Heat transfer by convection occurs when natural forces such as gravity and buoyancy (either positive or negative) due to a temperature gradient between a body and its fluidous environment, and possibly external forces such as a fan, cause the fluidous environment to flow about the body and transfer heat to or from that body. Heretofore, conductive heat transfer was the primary means of control and it was sought by placing one or more layers of an insulating material around the body. Insulation, however, is often expensive, not intended nor effective at dealing with controlling convective heat transfer, difficult to install, and can deteriorate over time. Moreover, some insulation materials, e.g. asbestos, have proven harmful to the environment and man.
Jaber et al., Optimal Location of a District-Heating Pipeline Within a Rectangular Duct, Applied Energy, 40, pp. 101-109 (1991), considered the problem of heat transfer in natural convection flow over an insulated horizontal hot-water pipe embedded within an air filled, relatively cold, rectangular air-filled duct. The data suggest an optimal configuration in terms of pipe location relative to the cavity walls which could result in a minimum rate of heat loss from the pipe. Similarly, Jaber et al, Optimal Thermal-Insulation Placement of District-Heating Pipes and Their Support Baffles in Air Filled Trenches, Applied Energy, 40, pp. 111-118 (1991), investigated the steady state heat-transfer across a cold, horizontal, rectangular cavity enclosing two relatively hot horizontal pipes. The data suggest that the minimum steady-state heat loss occurs when the two pipes were placed one above the other. The analysis suggests that effective thermal resistance can further be enhanced by physically supporting each pipe with a pair of low conductivity physical support structures which are termed baffles. The support structures form isolated air spaces in a closed environment. Jaber et al only deal with heated pipes located within cold ducts.
Neale et al, Steady State Heat Transfers Across an Obstructed Air-Filled Rectangular Cavity, Chem. Eng. Res. Des., 66, pp. 458-462 (1988) considered the problem of heat transfer from a hot horizontal pipe embedded inside a cold, horizontal, rectangular, air-filled duct. The pipe was assumed to be supported by two, low-conductivity, symmetrically-placed spacers that completely bridge the gap between the pipe and the walls of the duct and extend the length of the pipe. The article suggests that the presence of such spacers could improve the thermal resistance of the air-filled cavity over an unobstructed one. The article is limited to pipes located in a closed environment, i.e. an air-filled duct.
Lai, Improving Effectiveness of Pipe Insulation By Using Radial Baffles to Suppress Natural Convection, Int. J. Mass Heat Transfer, 36, pp. 899-906 (1993) discloses the use of baffles solely as an integral part of porous media insulation, i.e. located within the insulation. There is no suggestion of extending the baffles beyond the insulation to further reduce heat loss from the pipe.
Accordingly, there remains a need for improved control or reduction of heat transfer between a body and its fluidous environment without the need of bulky, expensive layers of insulating materials. There is a need to minimize heat transfer between a body, e.g. a pipe, and its environment without going to the extreme of placing the body in an air-filled cavity or isolated duct or for relocating the body.